Increase surveillance of tick-borne infections has shown that many individuals infected with Lyme disease have co-infections with Babesia microti (agent of human babesiosis) and Ehrlichia, both of which are potentially fatal in immunocompromised individuals and have been shown to impact blood transfusions. Since the treatment of B. microti infections (malaria-like intraerythrocytic parasite) is vastly different that Lyme disease there is a need for an accurate serology test to differentiate the two infections. The proposed studies will enable the development of an ELISA and Immunoblot test using B. microti recombinants in combination that will supplement the currently available Lyme disease test and eventually facilitate testing of blood donors. Development of such tests improves our ability to differentially diagnose tick-borne diseases and facilitates administration of the appropriate treatment. Advances have already been achieved at Corixa in identifying immunodominant recombinant antigens. This, in combination with collaborations with key investigators in the area of tick-borne diseases, blood banking and a leading reference laboratory for Lyme disease testing and access to their extensive serum bank should enable the goals and objectives of this proposal to be achieved. PROPOSED COMMERCIAL APPLICATION The proposed studies will lead to commercialization of diagnostic tests for use in the blood bank and reference laboratory. Such tests would provide for improved differential diagnosis of babesiosis in the presence of other tick-borne infections e.g. Lyme disease and Human Granulocytic Ehrlichiosis. The estimated market for such a test should be similar to that for Lyme disease testing both in the U.S. and worldwide. Current estimates for this market are 30-50 million dollars/year but could be greater if blood bank testing is mandated even on a regional basis.